Fiber cement building materials with low density additives

ABSTRACT

This invention relates to a formulation with the addition of low density additives of volcanic ash, hollow ceramic microspheres or a combination of microspheres and volcanic ash or other low density additives into cementitious cellulose fiber reinforced building materials. This formulation is advantageously lightweight or low density compared as compared to current fiber cement products without the increased moisture expansion and freeze-thaw degradation usually associated with the addition of lightweight inorganic materials to fiber cement mixes. The low density additives also give the material improved thermal dimensional stability.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/189,235, filed Mar. 14, 2000, the entirety of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to building materials and methods for making thesame, and more particularly to the addition of low density additives(LDA) into cementitious cellulose fiber-reinforced building materials.

2. Description of the Related Art

Fiber-reinforced cement (FRC) products such as water-resistant buildingsheets have been used for building since 1895. In recent historyreinforcing fibers used in such products have included not only asbestosfibers, but also cellulose fibers (see Australian Patent No. 515151),metal fibers, glass fibers and other natural and synthetic fibers.Typically, the density of such building sheets is from about 1.2-1.7g/cm³, the variation in density typically being achievable bycompression and dewatering of the fiber cement slurries used inmanufacture and by varying the amount of fiber used. At these densities,the cement based matrix has few voids, which results in lower waterabsorption which has usually been considered necessary for gooddurability performance of cement matrices.

The densities of fiber cement described above mean the products areheavier than timber based products of equal dimension and have reducedworkability. Workability encompasses the ease with which a board ishandled and installed. Therefore, fiber cement building products aremore difficult to cut, machine and nail than timber and timber basedproducts. In this regard, the density of natural timber sheets typicallyranges from about 0.7-0.9 g/cm³ for dry hardwoods and from about0.38-0.6 g/cm³ for dry softwoods. Thus, a density-modified fiber cementmaterial with density similar to timber may be expected to improveworkability and enable lighter, more nailable, easier to cut and easierto machine products to be manufactured. However, this would have to beachieved while retaining the durability, fire resistant, rot proof andwater resistant properties of fiber cement if the density modified fibercement is to be used in the same range of applications.

Prior art describes how lightweight inorganic powders can be added asdensity modifiers in cement or fiber-reinforced cement materials. Lowdensity additives for FRC products are defined as having a loose bulkdensity of about 0.8 g/cm³ (about 50 lbs./cu. ft.) or less. The typicallow density additives (LDA) used include low bulk density calciumsilicate hydrates (CSH), expanded polystyrene beads (EPS), expandedvermiculite, expanded perlite, expanded shale, and expanded clay. Thedensity modification of cement-based materials with such inorganicparticles is primarily achieved by introducing porosity into thematerial. Typically, the pore spaces are filled with water when thematerial is submerged in water or exposed to rain for a length of time.This causes these materials to have poorer wet to dry dimensionalstability (moisture resistance), a higher saturated mass, and poorfreeze-thaw resistance.

Accordingly, there is a need for a lightweight FRC building material andmethod for manufacturing the same with improved wet to dry dimensionalstability over that of typical density modified products. Secondly, thelightweight building material should maintain similar wet to drydimensional stability as that of FRC products without density modifiersif the density modified material is to be used in the same range ofapplications. In addition, it is highly preferred in some applicationsthat the material also have a low saturated mass, good freeze-thawresistance, and high temperature dimensional stability. Finally, it isalso desirable to have a FRC building product where lower ranges ofdensities closer to that of timber and timber based products can beachieved with improved durability.

SUMMARY OF THE INVENTION

Two low density additives have been evaluated that have properties moredesirable to FRC building materials than typical low density additives.These two low density additives are volcanic ash and hollow ceramicmicrospheres. One embodiment of the invention includes the addition ofvolcanic ash (VA) into an FRC building material. A second embodimentcomprises the addition of hollow ceramic microspheres (microspheres)into the FRC building material. A third embodiment incorporates theblending of microspheres with volcanic ash and/or other typical lowdensity additives into the FRC building material. The third embodimentwith the blend of microspheres and VA and/or other low density additivesmay be more preferable than the first embodiment with the introductionof volcanic ash by itself. The second embodiment with the addition ofmicrospheres by themselves may be more preferable than either the firstor third embodiments as described above, depending on the propertiesbeing considered for a particular application.

Compared to current FRC products, one advantage of the first embodimentwith volcanic ash is that it provides the product with low densities andimproved workability at an economical price, as well as improveddimensional stability over that of typical low density additives.

The second embodiment encompasses the addition of microspheres infiber-cement products. Compared to current FRC products, the benefits ofadding microspheres include the low density and improved workability ofthe product without increased moisture expansion or freeze-thawdegradation associated with the addition of lightweight inorganicmaterials to FRC mixes. Moreover, the addition of microspheres providesimproved thermal dimensional stability for FRC material.

The third embodiment relates to the addition of microspheres incombination with VA and/or other typical low density additives in FRCmaterial. Blending microspheres with other low density additives isadvantageous because lower density FRC products can be achieved withless weight percent addition (as compared to microspheres only) due tothe lower densities of VA and other typical LDA relative tomicrospheres. This also enables fiber cement products to achieve lowerdensity ranges to further improve workability, while microspheresminimize the adverse effects typical low density additives have onwet-to-dry dimensional stability and overall durability.

Thus, in one aspect of the present invention, a building material isprovided comprising a fiber-reinforced cement formulation and a lowdensity additive incorporated into the formulation. The addition of thelow density additive to the formulation lowers the density of thebuilding material as compared to a building material having anequivalent fiber-reinforced cement formulation without the low densityadditive, while at the same time the building material with the lowdensity additive has less than about a 20% increase in moistureexpansion as compared to a building material having an equivalentfiber-reinforced cement formulation without the low density additive.More preferably, the addition of the low density additive to theformulation lowers the density of the building material as compared to abuilding material having an equivalent fiber-reinforced cementformulation without the low density additive, while at the same time thelow density additive either maintains or decreases the moistureexpansion of the building material as compared to a building materialhaving an equivalent fiber-reinforced cement formulation without the lowdensity additive. The density of the building material is preferablyabout 1.2 g/cm³ or less.

In another aspect of the present invention, a building materialformulation is provided to form a building product. The formulationcomprises a hydraulic binder, an aggregate, fibers and volcanic ash. Inone embodiment, the volcanic ash improves the workability and lowers thedensity of the final building product by more than about 10% as comparedto a building product made from an equivalent formulation withoutvolcanic ash. In another embodiment, the formulation with volcanic ashhas a negligible difference in the moisture expansion of the finalproduct whereby the product either maintains or increases moistureexpansion by less than about 20% as compared to a building product madefrom an equivalent formulation without volcanic ash. For the degree ofdensity modification achieved, this moisture movement increase issurprisingly low. With nominally the same formulation ingredients, ithas been found that differences in moisture expansion for volcanic ashformulations exist. Such differences are primarily due to fluctuationsin the surface area of raw materials.

In another aspect of the present invention, a method of forming a lowdensity building material is provided. Hydraulic binder, aggregate,volcanic ash and water are mixed to create a slurry. The slurry isprocessed into a green shaped article. The green shaped article is curedto form the low density building material. In one embodiment, thearticle is cured by autoclaving. In another embodiment, the low densitybuilding material formed has a density of about 1.2 g/cm³ or less, and amoisture expansion of about 0.17% or less.

In another aspect of the present invention, a building materialformulation comprises a hydraulic binder, an aggregate, fibers andhollow ceramic microspheres. The final building material has a densityof about 1.2 g/cm³ or less. In one embodiment, about 4.1%-15% cellulosefibers are provided in the formulation. In one preferred embodiment, themicrospheres lower the density of the final building product by morethan about 15%, even more preferably more than about 30%, as compared toa building product made from an equivalent formulation withoutmicrospheres. In another embodiment, the microspheres decrease themoisture expansion of the final product as compared to a buildingproduct made from an equivalent formulation without microspheres,preferably by more than about 5%, more preferably by more than about10%. In one preferred embodiment, a combination of microspheres withother additional low density additives such as volcanic ash and/or lowbulk density CSH are provided in the formulation.

In another aspect of the present invention, a method of forming a lowdensity building material, comprising mixing hydraulic binder,aggregate, fibers, hollow ceramic microspheres and water to create aslurry. The slurry is processed into a green shaped article. The greenshaped article is cured to form the low density building material. Theresulting building material has a density of about 1.2 g/cm³ or less. Inone embodiment, more than about 4% fibers are mixed to create theslurry. In another embodiment, the article is cured by autoclaving.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of MIP pore size distribution for a Hatschekmanufactured board with and without hollow ceramic microspheres afterfreeze-thaw testing.

FIG. 2 is a graph of BET pore size distribution for a Hatschekmanufactured board with and without hollow ceramic microspheres afterfreeze-thaw testing.

FIG. 3 is an SEM photograph illustrating a Hatschek manufactured boardwith 10 wt. % hollow ceramic microspheres showing no degradation after147 freeze-thaw cycles.

FIG. 4 is a graph illustrating the relationship between low densityadditive addition, density and strength.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention describe afiber-reinforced cement building material incorporating at least one oftwo low density additives, hollow ceramic microspheres and/or volcanicash. It will be appreciated that these additives may be used not onlyfor the types of building materials described herein (i.e.,fiber-reinforced materials), but may be used for other buildingmaterials as well. In addition, various combinations of microspheresand/or volcanic ash with other density modifiers are also contemplatedto lower the density and improve the overall performance of the buildingmaterial. Furthermore, other low density additives similar to hollowceramic microspheres and volcanic ash that achieve the properties oflowering density while maintaining or decreasing moisture expansion ofthe final product, as well as improving workability, durability andother properties (as discussed below), are also contemplated as beingwithin the scope of this invention.

1. First Embodiment Volcanic Ash

In a first embodiment, this invention relates to the addition ofvolcanic ash into cementitious cellulose fiber reinforced buildingmaterials. Volcanic ash is also commonly referred to as “airborneperlite”, “pumice” or “pumicsite”. Volcanic ash is typically a naturalglass derived from the magma of volcanoes during an eruption. Volcanicash is a relatively lightweight sand sediment formed by the cooling ofhigh temperature magma, giving rise to a material comprising about 30wt. % crystalline minerals and 70 wt. % amorphous volcanic ash glass. Ithas a typical bulk density of about 25-75 lbs./cu. ft. Usually thisvolcanic ash is expanded with the introduction of heat to change themorphology and achieve a lighter material with a typical bulk densityranging from about 2-25 lbs./cu. ft. Expanded volcanic ash can have awide range of particle sizes from less than about 10 microns up to about425 microns, with median particles sizes ranging between about 20 to 100microns. The chemical composition primarily consists of silica (SiO₂),alumina (Al₂O₃), and potassium oxides (K₂O).

Volcanic ash or expanded volcanic ash is available through supplierssuch as Tufflite Inc. of Phoenix, Ariz.; California Industrial Mineralsof Friant, Calif.; US Pumice of Chatsworth, Calif.; Amcor Precast ofIdaho Falls, Id.; Hess Pumice Products of Malad City, Id.; KansasMinerals Inc. of Mankato, Kans.; Calvert Corporation of Norton, Kans.;Copar Pumice Company of Espanola, N.Mex.; C.R. Minerals of Santa F;N.Mex; Utility Block of Alburquerque N.Mex.; and Cascade Pumice of Bend,Oreg.

One preferred formulation of the first embodiment of the presentinvention comprises a hydraulic binder, aggregate, fiber, volcanic ashand additives. The hydraulic binder is preferably Portland cement butcan also be, but is not limited to, high alumina cement, lime, groundgranulated blast furnace slag cement and gypsum plasters or mixturesthereof. The aggregate is preferably ground silica sand but can also be,but is not limited to, amorphous silica, diatomaceous earth, rice hullash, blast furnace slag, granulated slag, steel slag, mineral oxides,mineral hydroxides, clays, magnasite or dolomite, polymeric beads, metaloxides and hydroxides, or mixtures thereof. The fiber is preferablycellulose wood pulp but can also be, but is not limited to, ceramicfiber, glass fiber, mineral wool, steel fiber, and synthetic polymerfibers such as polyamides, polyester, polypropylene, polymethylpentene,polyacrylonitrile, polyacrylamide, viscose, nylon, PVC, PVA, rayon,glass ceramic, carbon or any mixtures thereof. The additives caninclude, but are not limited to, silica fume, geothermal silica, fireretardant, thickeners, pigments, colorants, plasticisers, dispersants,foaming agents, flocculating agents, water-proofing agents, organicdensity modifiers, aluminum powder, kaolin, alumina trihydrate, mica,metakaolin, calcium carbonate, wollastonite, polymeric resin emulsions,or mixtures thereof.

Volcanic ash can be used in a variety of building products all havingdifferent proportions of hydraulic binder, aggregate, volcanic ash andadditives to obtain optimal properties for a particular application(e.g., siding, roofing, trim, soffit, backerboard for tile underlay,etc.). It will be appreciated that the percentage of volcanic ash may bevaried depending on the desired application. One preferred compositionmay include about 5%-80% Portland cement, about 0%-80% silica, about4.1%-15% cellulose, about 0%-10% additives and about 2%-50% volcanicash. One particular example of a typical formulation with volcanic ashis as follows:

Portland Cement (binder) 28% Silica (aggregate) 54% Cellulose (fiber) 7%Metal Hydroxide (additive) 4% Volcanic Ash (LDA) 7%.Preferably, the cement and silica have a fineness index of about 200 to450 m²/kg. The fineness index for both cement and silica is tested inaccordance with ASTM C204-96a.

The material may be formed into a green shaped article from a waterbornemixture or slurry by a number of conventional processes as would beknown to one of skill in the art, such as the:

-   -   Hatschek sheet process;    -   Mazza pipe process;    -   Magnani process;    -   Injection molding;    -   Extrusion;    -   Hand lay-up;    -   Molding;    -   Casting;    -   Filter pressing;    -   Flow on machine, roll forming, etc.        with or without post pressing. The processing steps and        parameters used to achieve the final product using a Hatschek        process are described in Australian Patent No. 515151.

The material is preferably pre-cured for up to 80 hours, most preferably24 hours or less, to establish the formulation to set. The material isthen air-cured (approximately 28 days) or more preferably, autoclaved atan elevated temperature and pressure in a steam saturated environment at120 to 180° C. for 3 to 30 hours, most preferably 24 hours or less. Thelength and time chosen for curing is dependent on the formulation, themanufacturing process, and the form of the article.

Test Results

Density & Workability

The addition of volcanic ash in fiber cement materials lowers densityand improves overall workability properties at an economical price whilereducing the moisture expansion observed with that of typical lowdensity additives. Products with volcanic ash are lighter, and thereforeeasier to handle, nail, and score and snap to the desired dimensions.Formulations with volcanic ash also reduce edge cracking or crumbling(if any) when the board is nailed close to the edge (e.g., ⅜-¾″). Tables1 and 2 below illustrate FRC formulations and test results for theseformulations, more particularly demonstrating the advantages of addingvolcanic ash to lower density and improve workability.

TABLE 1 Formulations for Table 2 Test Results Portland Expanded CementMetal Volcanic Formula Hydraulic Silica Cellulose Hydroxide AshIdentification Binder Aggregate Fiber Additive LDA B 28.7 60.3 7.0 4.0 K28.7 52.8 7.0 4.0 7.5

TABLE 2 Comparison of Properties With and Without Volcanic AshFormulation Formulation K¹ 7.5% B Control Test Method Volcanic Ash NoLDA Oven Dry (O.D.) Density 1.11 1.34 (g/cm³) Nail Penetration(Equilibrium conditions)² mm. of nail in material 45.4 33.0 50 mm (2in.) = length of nail 1.1 1.0 Standard Deviation ¹7.5 wt. % of theaggregate from the control, Formulation B, has been displaced by 7.5%Volcanic Ash for Formulation K. ²Equilibrium conditions - samples areconditioned in a controlled atmosphere of 73 ± 4° F. and 50 ± 5%humidity. Refer to text below for definition and description of nailpenetration test.

Table 2 above compares test results of 10″×10″ filter pressed prototypeboards with and without volcanic ash. Prototype boards are produced bymixing the desired formulation with a Hobart Mixer to form a homogenousslurry. The slurry is then compressed between two steel dewateringplates at 3500 psi for one minute with a Wabash Press (model #PC-75-4TM)to form a monolithic sheet. The slurry is supported with steel wire meshscreens (30 to 40 US mesh) placed underneath and on top of the slurrymix within the steel frame mold. The monolithic sheet is then pre-curedfor a minimum of about 12 hours and autoclaved at an elevatedtemperature and pressure in a steam saturated environment at 150° C. forabout 12 hours.

In Table 2, Formulation K with 7.5 wt. % volcanic ash lowers the densityby about 17% from 1.34 g/cm³ to 1.11 g/cm³ when compared to anequivalent formulation, Formulation B, the control formulation, withoutvolcanic ash. An equivalent formulation is herein defined as one inwhich the preferred LDA (e.g., volcanic ash) is displaced by anequivalent percentage of binder, aggregate and/or additives, and morepreferably is displaced by an equivalent percentage of aggregate. Thislowered density also improves the nailability, or ease of driving a nailinto the board. Testing showed an increase in nail penetration from 33.0mm to 45.4 mm, where 50 mm represents the length of the nail andtherefore the maximum nail penetration attainable. Nail penetrationtesting consists of nailing a layered stack of board using a PaslodeImpulse® cordless framing hardware gun (positive placement) to ensureconsistent nailing pressure. The layered stack typically comprises ¼-½″thick board stacked to a height greater than the length of the nail (2in. or 50 mm). Senco 6d galvanized clipped head nails (part #GC21AABN)were used.

Thus, in one embodiment, as compared to a typical building sheet havinga density of about 1.3 g/cm³, the building material formulationdescribed above results in a final product having a density of less thanabout 1.2 g/cm³. More preferably, the addition of volcanic ash to thebuilding material formulation can preferably be adjusted to give a finalproduct density of about 1.2 g/cm³ or less, or about a 10% or morereduction in density as compared to an equivalent formulation withoutvolcanic ash. It is further contemplated that larger additions ofvolcanic ash will further lower the density of the building product.

Wet-Dry Dimensional Stability

Cured fiber cement formulations with conventional density modifiers haveincreased moisture expansion and increased moisture absorption on apercentage weight increase basis compared to FRC formulations with noLDA. One advantage of the first embodiment over prior art is that theaddition of volcanic ash attains the desired density and workabilitywith less moisture expansion than other conventional low densityadditives when introduced on a similar weight percent basis. Wet-drydimensional stability is desired in building products for quality anddurability of the installed product, especially in exterior applicationssubject to severe climatic changes. Good dimensional stability minimizesany gaps that may open between sheets or lengths of building panel orplank. Good dimensional stability also reduces the likelihood of sheetcracking due to developed stress between the dimensionally changingpanel or plank and the supporting framework that the product isfastened.

Tables 3 and 4 below illustrate FRC formulations and test results forthese formulations, more particularly demonstrating the advantages ofadding volcanic ash to lower density while minimizing moisture expansiontypical of other low density additives added on an equivalent weightbasis.

TABLE 3 Formulations for Table 4 Test Results Portland Expanded CementMetal Volcanic Expanded Formula Hydraulic Silica Cellulose Hydroxide AshPerlite Identification Binder Aggregate Fiber Additive LDA LDA B 28.760.3 7.0 4.0 K 28.7 52.8 7.0 4.0 7.5 L 28.7 55.3 7.0 4.0 5.0

TABLE 4 Moisture Expansion¹ Comparison of Volcanic Ash & Perlite. O.D.Moisture % Moisture Formul- Density Expansion Expansion Increase ationDescription (g/cm³) % from Control B² Control-No LDA 1.33 0.18 ± 0.02 K³7.5% VA 1.11 0.17 ± −5.5 0.02 L 5% Perlite 1.22 0.22 ± 22.2 0.02¹Moisture expansion is the change in product length from saturated tooven dry conditions. The % change moisture expansion equation is:$\frac{{Length}_{initial} - {Length}_{final}}{{Length}_{final}} \times 100.$²Throughout this description of the preferred embodiments Formulation Bis used for the control. However, as no one sample incorporatingFormulation B is used for all of the tests, nominal differences may befound in the test results for any one sample. ³7.5 wt. % of theaggregate from the control, Formulation B, has been displaced by 7.5%Volcanic Ash for Formulation K.

Table 4 above displays test results of 10″×10″ filter-pressed prototypeboards comparing formulations with 7.5 wt. % volcanic ash and 5.0%perlite (Harborlite 2000 from Harborlite Corp.), a typical low densityadditive. Formulation L with 5.0% perlite has a 22.2% increase inmoisture expansion from the control whereas Formulation K with 7.5%volcanic ash actually shows a decrease of more than about 5% in moistureexpansion from the control.

Thus, the addition of volcanic ash provides better dimensional stabilitythan typical density modifiers at equivalent or lower weight percentadditions. This allows volcanic ash to achieve lower densities andbetter workability properties with equivalent or higher additions ofvolcanic ash relative to conventional low density additives.

More preferably, the addition of volcanic ash can be adjusted to show anegligible difference in moisture expansion as compared to an equivalentformulation without volcanic ash. In one embodiment, the volcanic ashpreferably will increase the moisture expansion of the final product byless than about 20% compared to a building product formed from anequivalent formulation without volcanic ash, and will more preferablydecrease the moisture expansion of the final product. In one preferredembodiment, the moisture expansion of a building product made from aformulation having volcanic ash is about 0.17% or less.

2. Second Embodiment Hollow Ceramic Microspheres

A second embodiment of this invention encompasses the addition of hollowceramic microspheres into cementitious cellulose fiber-reinforcedbuilding materials. This second embodiment with hollow ceramicmicrospheres may be preferred over the first embodiment includingvolcanic ash because the addition of microspheres in FRC materials haseven better moisture resistance coupled with other durabilityadvantages, including freeze-thaw resistance, and thermal dimensionalstability. It will be appreciated that the preferred embodiments for thesecond embodiment are not limited to these types of microspheres orbuilding materials. Thus, other types of fillers and building materialsare also contemplated.

Microspheres can be natural, synthetic or a by-product. The material canbe crystalline but is more typically amorphous or glass. One preferredtype of microspheres are hollow ceramic microspheres commonly known ascenospheres. Cenospheres are a coal ash by-product that is typicallyseparated from fly ash by a floatation process where the spheres floatto the surface of water from clarifiers, ponds or lakes. Themicrospheres are available, for example, under the namesExtendospheres®, Recyclospheres® and Zeeospheres®, and are availablefrom suppliers such as PQ Corporation of Chattanooga, Tennessee; ZeelanIndustries Inc./3M of St. Paul, Minn.; Sphere Service, Inc. of OakRidge, Tenn.; and Advanced Cement Technologies (A.C.T.) of Blaine, Wash.

The microspheres have typical particle sizes ranging from about 12 to300 microns, with median particle sizes ranging about 80 to 120 microns.These sizes can, of course, vary between samples. The preferredmicrospheres typically contain about 62%-65% silica (SiO₂), about23%-26% alumina (Al₂O₃) and about 3.0% to 4.0% iron oxides (Fe₂O₃). Whenintroduced into a building material, the microspheres introduce pores inthe material that may not readily fill with water which is advantageousto the material because of a lower saturated mass, improved wet to drydimensional stability and improved freeze-thaw resistance.

One preferred formulation of the second embodiment comprises a hydraulicbinder, aggregate, fiber, hollow ceramic microspheres and additives. Itwill be appreciated that the various components of the preferredformulation for the second embodiment can include any of theaforementioned materials listed for each component in the firstembodiment. The material may also be produced by a number ofconventional processes and curing conditions as listed and described inthe first embodiment. If applicable, the preferences of the rawmaterials, processes, steps or conditions are similar to that of thefirst embodiment.

The microspheres can be used in a variety of building products allhaving different proportions of hydraulic binder, aggregate,microspheres and additives to obtain optimal properties for a particularapplication (e.g., siding, roofing, trim, soffit, backerboard for tileunderlay, etc.). One preferred composition may include about 5%-80%Portland cement, about 0%-80% silica, about 4.1%-15% cellulose, about0%-10% additives and about 2%-90% microspheres. One particular exampleof a typical formulation with microspheres is as follows:

Portland Cement (binder) 28.7% Silica (aggregate) 50.3% Cellulose(fiber)   7% Metal Hydroxide (additive)   4% Microspheres (LDA)    10%.

It will be appreciated that the percentage of microspheres may be varieddepending on the desired application. For instance, high additionpercentages (up to about 90 wt. %) of microspheres may be suitable forbuilding materials and systems that require some type of fire resistancerating. The high addition of microspheres provides the material with lowthermal shrinkage.

Test Results

Density

Lowering the density with microspheres improves the overall workabilityof thicker products without compromising the advantages fiber cementproducts offer with regard to durability (i.e., dimensional stability)and structural integrity. These attributes are particularly advantageousfor product thicknesses above about three eighths of an inch (>⅜″). Theproducts with microspheres are lighter and therefore easier to handle.Secondly, products with microspheres are easier to nail and score/snapto the desired dimension. Furthermore, microsphere formulations reduceedge cracking or crumbling (if any) when the board is nailed close tothe edge (e.g., ⅜-⅝″).

Tables 5 and 6 below display formulations and test results for FRCformulations, more particularly illustrating the advantages of addingmicrospheres to a formulation to improve density and workability.

TABLE 5 Formulations for Table 6 Test Results Portland Cement MetalMicro- Formula Hydraulic Silica Cellulose Hydroxide spheresIdentification Binder Aggregate Fiber Additive LDA B 28.7 60.3 7.0 4.0 A28.7 50.3 7.0 4.0 10.0

TABLE 6 Comparison of Properties With and Without MicrospheresFormulation B Formulation A¹ Control Test Method 10% Microspheres No LDADensity 1.16 1.39 (Equilibrium Conditions)² (g/cm³) Nail Penetration(Equilibrium conditions) mm. of nail in material 47.0 31.7 50 mm (2 in.)= length of nail 0.9 1.4 standard deviation ¹10% microspheres inFormulation A replace 10% of the aggregate in the control, FormulationB. ²Equilibrium conditions - samples are conditioned in a controlledatmosphere of 73 ± 4° F. and 50 ± 5% humidity.

Table 6 displays test results of 3′×5′ Hatschek manufactured board forFormulations A and B. Formulation A with 10 wt. % microspheres reducesthe density by about 15% from 1.39 g/cm³ to 1.16 g/cm³ when compared toan equivalent formulation without microspheres (Formulation B). Inaddition, the ease of driving a nail into the board is improved. Testingrevealed an increase in nail penetration from 31.7 mm to 47.0 mm, where50 mm represents the length of the nail and the maximum nail penetrationattainable.

Overall, testing of prototypes and products produced from trials hasrevealed about a 15% decrease in density for every 10% addition ofmicrospheres and significant improvements in nailing. Thus, the additionof microspheres may advantageously be used to reduce the density of FRCbuilding material by more than about 15%, even more preferably more thanabout 30%, as compared to an equivalent formulation withoutmicrospheres. The present inventors contemplate that with the additionof microspheres, the density of the material can be reduced to about 0.9g/cm³ (see Table 10 below), and more preferably, even as low as about0.5 g/cm³.

Wet-Dry Dimensional Stability

As stated earlier, cured fiber cement formulations with conventionaldensity modifiers have increased moisture expansion and increasedmoisture absorption on a percentage weight increase basis. One advantageof the preferred embodiments over prior art is that the addition ofmicrospheres to reduce density does not increase moisture expansion fromwet to dry. This is useful for a number of reasons previously mentionedin the first embodiment.

Table 7 below displays test results of 3′×5′ Hatschek manufactured boardwith and without microspheres. Formulation A with 10% microspheresmaintains, or more preferably reduces moisture expansion from that ofFormulation B without microspheres. Formulations A and B are in Table 5above.

TABLE 7 Comparison of Moisture Expansion With and Without MicrospheresFormulation B Formulation A¹ Control Test Method 10% Microspheres No LDADensity 1.16 1.39 (Equilibrium Conditions)² (g/cm³) Moisture Expansion0.15 ± 0.02 0.16 ± 0.02 % Change ¹10% microspheres in Formulation Areplace 10% of the aggregate in the control, Formulation B. ²Equilibriumconditions - samples are conditioned in a controlled atmosphere of 73 ±4° F. and 50 ± 5% humidity.Tables 8-10 below display formulations and test results for 10″×10″filter pressed prototype boards comparing microspheres with conventionaldensity modifiers that do increase moisture expansion. Conventionaldensity modifiers include low bulk density calcium silicate hydrate(CSH), and expanded polystyrene, vermiculite, perlite, shale or clay.

TABLE 8 Formulations for Tables 9 and 10 Test Results Low Portland BulkCement Metal Micro- Density Expanded Formula Hydraulic Silica CelluloseHydroxide spheres CSH Perlite Identification Binder Aggregate FiberAdditive LDA LDA LDA B 28.7 60.3 7.0 4.0 C 35.2 52.8 8.0 4.0 D 26.8 40.28.0 25.0 E 26.8 40.2 8.0 25.0 F 28.7 55.3 7.0 4.0 5.0

Table 9 data below displays a conventional low density additive, lowbulk density CSH (Silasorb from Celite Corp.), at a 5% load thatincreases moisture expansion from that of the control, Formulation B.

TABLE 9 Moisture Expansion of Low Bulk Density CSH Equilibrium FormulaDensity¹ Moisture Identification Description (g/cm³) Expansion % BControl 1.41 0.162 ± 0.02 F² 5.0% low bulk 1.27 0.188 ± 0.02 density CSH¹Equilibrium conditions - samples are conditioned in a controlledatmosphere of 73 ± 4° F. and 50 ± 5% humidity ²5% low bulk density CSHin Formulation F replaces 5% of the aggregate in the control,Formulation B.

Table 10 below compares two formulations with the same base formula, onewith 25 wt. % microspheres and the other with 25 wt. % perlite (Aztec XXfrom Aztec Perlite). Both the perlite and microsphere formulationsdecrease the density of control Formulation C from 1.3 g/cm³ to around0.9 g/cm³, but moisture expansion increases with the perlite formulationand decreases with the microsphere formulation.

TABLE 10 Moisture Expansion Comparison of Microspheres & Perlite.Equilibrium Density¹ Moisture Formulation Description (g/cm³) Expansion% C Control 1.31 0.230 ± 0.02 D² 25% Microspheres 0.90 0.202 ± 0.02 E²25% Perlite 0.89 0.275 ± 0.02 ¹Equilibrium conditions - samples areconditioned in a controlled atmosphere of 73 ± 4° F. and 50 ± 5%humidity ²For formulations D and E, microspheres displace both theaggregate and hydraulic binder in the control, Formulation C.

Thus, the addition of microspheres to the fiber cement formulation hasthe effect of maintaining or reducing moisture expansion of the finalproduct. Preferably, the addition of microspheres can be adjusted toreduce the moisture expansion by about 5%, more preferably by about 10%or more, as compared to an equivalent formulation without microspheres.

Freeze-Thaw Resistance

Freeze-thaw resistance refers to a material's resistance to damage whenexposed to repeated cycles of freezing and thawing. For instance,concrete can be damaged by frost, and especially by repeated cycles offreezing and thawing. Damage usually begins with flaking at the surface,and gradually extends inward, though deep cracks may occur. Damageassociated with freezing generally does not occur unless a sufficientquantity of water is present in the pores, and is minimal in denseconcrete of low water-to-cement ratio and low permeability.

Similar to high density concrete, freeze-thaw damage is minimal inhigh-density fiber cement. In the preferred embodiments, the addition ofmicrospheres into a FRC formulation produces a lower density curedproduct that maintains freeze-thaw resistance, unlike prior art wheredensity modifiers added to the formulation reduce a material'sfreeze-thaw resistance.

FIGS. 1 and 2 display pore size distribution graphs of 3′×5′ Hatschekmanufactured board using MIP (mercury intrusion porosimetry) and BET(Brunauer, Emmett and Teller) methods. There is less change in pore sizedistribution for Formulation A with 10 wt. % microspheres after 147freeze-thaw cycles than Formulation B without microspheres after 126cycles. This demonstrates the microsphere formulation's resistance tostructural change typical of freeze-thaw damage. To further support themicrosphere formulation's resistance to freeze-thaw damage, FIG. 3displays a SEM (scanning electron microscope) picture of a Hatschekmanufactured board (3′×5′) with 10 wt. % microspheres showing no signsof degradation after 147 freeze-thaw cycles whereas other wood cementcomposites would typically have degradation at this stage.

Freeze-thaw testing of FIG. 3 was performed in accordance with ASTM(American Standard Test Method) C666A titled “Standard Test Method forResistance of Concrete to Rapid Freezing and Thawing.” This test methodhas two different procedures, A or B. Procedure A was followed, meaningsamples were submerged in water for both rapid freezing and thawing asopposed to rapid freezing in air and rapid thawing in water (procedureB). Samples are periodically removed from freeze-thaw cycling andvisually inspected for degradation such as cracking, moisture expansion,sponginess/wetting throughout the sample, and overall structuralintegrity. Samples are moved from freeze-thaw cycling when the degree ofdegradation is such that the sample does not hold together and wouldtherefore not be functional as a building product.

High Temperature Dimensional Stability

Reducing a building material's thermal shrinkage prevents hightemperature stresses and strains from occurring on building components.This improved thermal-dimensional stability allows building componentsin building fires to maintain a shield to fire without cracking, fallingapart and allowing fire to spread quickly.

Tables 11 and 12 below display FRC formulations and test results for10″×10″ filter-pressed prototype boards, more particularly illustratingthe advantages of adding microspheres to a formulation to improve hightemperature dimensional stability.

TABLE 11 Formulations for Table 12 Test Results Portland Cement MetalMicro- Low Bulk Formula Hydraulic Silica Cellulose Hydroxide spheresDensity CSH Identification Binder Aggregate Fiber Additive LDA LDA A28.7 50.3 7.0 4.0 10.0 B 28.7 60.3 7.0 4.0 F 28.7 55.3 7.0 4.0 5.0 G28.7 50.3 7.0 4.0 10.0 H 28.7 40.3 7.0 4.0 20.0

TABLE 12 Thermal Shrinkage Comparison of Microspheres & Low Bulk DensityCSH Equilibrium Thermal Density² Shrinkage¹ Formulation Description(g/cm³) (%) B Control 1.41 3.07 F³  5.0% low bulk density CSH 1.21 7.27G³ 10.0% low bulk density CSH 1.15 8.09 A³ 10.0% microspheres 1.15 4.41H³ 20.0% microspheres 1.01 4.21 ¹Refer to text below for description ofthermal shrinkage test. ²Equilibrium conditions-samples are conditionedin a controlled atmosphere of 73 ± 4° F. and 50 ± 5% humidity. ³Thepercent LDA in formulations F, G, A & H replace an equivalent percent ofaggregate in the control, Formulation B.

At lower load levels (e.g., about 10-20%), microspheres minimize thehigh temperature thermal shrinkage that occurs when typical inorganicdensity modifiers are introduced in fiber-cement formulations. Table 12displays results of the percent thermal shrinkage obtained forFormulation A with 10 wt. % microspheres versus Formulation G with 10 wt% low bulk density CSH (Silasorb from Celite Corp). Compared to thecontrol (Formulation B), both formulations reduce density from about 1.4to 1.15 g/cm³, but the formulation with low bulk density CSH has almosttwice the thermal shrinkage as the formulation with microspheres.Moreover, Formulation H with 20.0 wt. % microspheres and a density ofabout 1.0 g/cm³ has over 40% less thermal shrinkage than Formulation Fwith only 5.0% low bulk density CSH (Silasorb from Celite Corp.) and ahigher density of about 1.2 g/cm³.

High temperature thermal shrinkages were determined using aThermomechanical Analyzer (TMA). Samples were cut to 10 by 25 mm with upto 12 mm thickness. The temperature of the saturated samples was rampedup at a rate of 20° C./minute to 950° C. and sample dimensions weremeasured with a macroexpansion probe. Thermal shrinkage was taken as theoverall dimensional change from 25° to 950° C., and reported as apercentage of total initial length.

Another advantage of using microspheres in fiber-cement formulations isthermal shrinkage decreases as microsphere additions increase. Thermalshrinkage with microspheres is inversely proportional to the weightpercent added, whereas thermal shrinkage with conventional densitymodifiers is directly proportional to the weight percent added. Thus,formulations with higher additions of microspheres (up to about 90 wt.%) have lower thermal shrinkage than formulations with lower additions(up to about 20 wt. %).

Table 13 below provides formulations with high additions of microspheresand Table 14 provides the high temperature thermal shrinkage results.Formulations I and J with 70 and 90 wt. % microsphere additions producethermal shrinkage results of about 2.7% and 1.1%, respectively. Thermalshrinkage for Formulations I and J were determined by cutting samplesapproximately 10×10×40 mm long, oven drying, firing for one hour at1000° C. with a muffle furnace, and allowing to cool to oven dryconditions. The percent thermal shrinkage was determined by measuringthe overall difference in length from oven dry to 1000° C., and dividingby the initial oven dry length.

TABLE 13 Formulations For Table 14 Results Portland Cement SilicaFormula Hydraulic Fume Cellulose Microspheres Identification BinderAggregate Fiber LDA I 26.2 2.9 0.9 70.0 J 8.7 1.0 0.3 90.0

TABLE 14 Thermal Shrinkage of High-Addition Microsphere FormulationsFormula Thermal Identification Shrinkage % I 2.7 J 1.1

Thus, in an embodiment where 20% microspheres are used in the fibercement formulation, the thermal shrinkage of the final product ascompared to an equivalent product made from a formulation withoutmicrospheres increases by less than about 50%. As described above, withincreasing percentages of microspheres, the percent thermal shrinkagedecreases, even to a point where, as compared to a product withoutmicrospheres, the final product with microspheres exhibits a lowerthermal shrinkage, preferably lower from about 10% to about 70%. Moreparticularly, the thermal shrinkage of the product with microspheres ispreferably less than about 4%.

3. Third Embodiment Microspheres and Other Additives

A third embodiment of this invention relates to the addition of hollowceramic microspheres in combination with volcanic ash and/or other lowdensity additives in cementitious cellulose fiber-reinforced buildingmaterials. Descriptions of volcanic ash and hollow ceramic microspheresare found in the detailed descriptions of the first and secondembodiments, respectively. The third embodiment with a blend ofmicrospheres and low density additives may be more preferable than thefirst embodiment with VA given FRC products can achieve a lower range ofdensities with improved moisture resistance and durability properties.However, the second embodiment with the independent addition ofmicrospheres may be preferable to this third embodiment because of thesuperlative durability properties offered by the independent addition ofmicrospheres. The preference of the second embodiment to the thirdembodiment is dependent on the relative importance of durability in aparticular application.

Similar to the first and second embodiments, one preferred formulationof the third embodiment comprises of a hydraulic binder, aggregate,fiber, hollow ceramic microspheres, low density additives and otheradditives. It will be appreciated that the various components of thethird embodiment can include any of the aforementioned materials listedfor each component in the first embodiment. The third embodiment mayalso be produced by a number of conventional processes and curingconditions as listed and described in the first embodiment. Ifapplicable, the preferences of the raw materials, processes, steps orconditions are similar to that of the first embodiment.

The blending of microspheres with VA and/or low density additives can beused in a variety of building products all having different proportionsof hydraulic binder, aggregate, low density additives, and otheradditives to obtain optimal properties for the particular application(e.g., siding, roofing, trim, soffit, backerboard for tile underlay,etc.). One preferred composition of the third embodiment could includeabout 5%-80% Portland cement, about 0%-80% silica, about 4.1%-15%cellulose, about 0%-10% additives and about 2%-60% microspheres andother typical LDA. One particular example of a typical formulation witha blend of microspheres and a typical low density additive is asfollows:

Portland Cement (binder) 28.7% Silica (aggregate) 50.3% Cellulose(fiber)   7% Metal Hydroxide (additive)   4% Microspheres (LDA)   10%Volcanic Ash (LDA)   5%

It will be appreciated that the percentage of microspheres and otherLDA's including VA may be varied depending on the desired application.

Test Results

Lower Densities with Durability

There are several advantages to blending microspheres with VA or othertypical low density modifiers such as low bulk density CSH, or expandedpolystyrene beads, clay, vermiculite, perlite, and shale. One advantageis that an equivalent or lower density can be achieved with less totalweight percent addition (than microspheres only) given the lowerdensities of VA and other typical LDA compared to microspheres. Thelower addition rates with the blend are more economical, and themicrospheres minimize moisture expansion associated with the addition oftypical inorganic density modifiers. Another advantage to blendingmicrospheres with other typical low density additives is that FRCproducts can achieve lower density ranges and still maintain sufficientproduct strength for handling. Thus, higher load levels (on a percentweight basis) of the combination of microspheres and other LDA can beadded while minimizing the adverse effects typical low density additiveshave on dimensional stability and overall durability.

The addition of low density additives in all of the embodimentsdescribed herein is not the only means of reducing density in cementbased formulations, however. Formulations consisting of cement andaggregate without fiber or low density additives have densitiestypically ranging from about 1.8 to 2.1 g/cm³. Adding fiber to cementformulations is advantageous because fiber also lowers density inaddition to providing strength and products suitable for nailing.Densities for fiber cement formulations with greater than about 4 wt. %fiber typically range from about 1.2 to 1.4 g/cm³. It has been foundthat FRC formulations with about 4 wt. % or less fiber do not havesufficient strength and ductility for installation. These FRC productsare often too brittle and nailing produces cracks or blowouts duringinstallation. Alternatively, fiber additions greater than about 15 wt. %may in some applications be undesirable because fiber in FRCformulations contributes to moisture expansion, increased permeability,and overall compromises in durability.

Thus, the right balance of fiber is advantageously determined for a FRCproduct, which is dependent on the thickness and shape of the particularproduct. In one embodiment, fiber percentages of about 4.1% to 15% arepreferable. Low density additives are added to the FRC formulation toprovide additional reductions in density from that of the fiberaddition. However, in general, the higher the addition of LDA, the lowerthe strength properties of the FRC product. Therefore, LDA additions arelimited because FRC products should preferably maintain a minimumstrength for sufficient handling and installation. The maximum LDAaddition is dependent on a multitude of factors such as the LDA, theload level of the specific LDA, and the shape of the particular FRCproduct. The minimum strength required is also dependent on the FRCproduct's shape and thickness. FIG. 4 displays a typical relationship ofmicrosphere wt. % additions to density and strength of 10″×10″filter-pressed prototype boards.

Tables 15-17 below illustrate FRC formulations and test results of10″×10″ filter-pressed prototype boards, more particularly illustratingthe advantages of blending microspheres with other low-density additivesto achieve lower density ranges and improve durability.

TABLE 15 Formulations for Tables 16 and 17 Portland Cement Metal Micro-Low Bulk Formula Hydraulic Silica Cellulose Hydroxide spheres DensityCSH Identification Binder Aggregate Fiber Additive LDA LDA B 28.7 60.37.0 4.0 G 28.7 50.3 7.0 4.0 10.0 M 28.0 49.0 7.0 4.0 12.0 N 28.4 49.67.0 4.0 6.0 5.0 O 28.7 51.3 7.0 4.0 6.0 3.0

Table 16 compares the densities of Formulation M with 12 wt. %microspheres, Formulation O with a 9 wt. % blend of microspheres and lowbulk density CSH, and the control without low density additives. The lowbulk density CSH used in Formulation O is produced by James Hardie usinga process with silica, lime and water that results in a low bulk densitymaterial that is substantially CSH in tobermorite form. Further detailsare described in U.S. patent application Ser. No. 09/058,444 filed Apr.9, 1998, the entirety of which is hereby incorporated by reference.Relative to the control, the decreases in density for Formulations M andO are not significantly different, but the total addition of low densityadditives with the blend (Formulation O) is 3% less than formulation Mwith only microspheres. For Formulations M and O, the subtle differencesin wt. % of hydraulic binder and aggregate do not have an impact ondensity properties.

TABLE 16 Density Comparisons Formula O.D. Density IdentificationDescription (g/cm³) B Control-No LDA 1.31 M¹ 12% Microspheres 1.09 O¹ 6% Microspheres 1.11  3% Low Bulk Density CSH ¹The percent LDA inFormulations M and O replace an equivalent percent of aggregate and/orbinder in the control with no LDA, Formulation B.

Table 17 below displays test results of 10″×10″ filter-pressed prototypeboards with four formulations containing variances primarily only inadditions of various low density additives, and a control without anylow density additives. Results show that Formulation M with 12 wt. %microspheres reduces density from that of the control from 1.35 g/cm³ to1.16 g/cm³, but Formulation N with 11 wt. % addition of themicrospheres/low bulk density CSH (Silasorb from Celite) blend lowersthe density further to 1.10 g/cm³. Moreover, moisture expansion forFormulation N with the 11 wt. % microspheres/low bulk density CSH blendand the control without low density additives is not significantlydifferent at 0.167 and 0.163%, respectively. In comparison, FormulationG with only 10 wt. % low bulk density CSH provides about the samedensity as Formulation N's 11 wt. % blend, but with a notably highermoisture expansion of 0.197%. The subtle wt. % differences of hydraulicbinder and aggregate in the formulations do not have an impact ondensity or moisture expansion properties.

TABLE 17 Moisture Expansion Comparisons O.D. Formula Density MoistureIdentification Description (g/cm³) Expansion % B Control-No LDA 1.350.163 ± 0.02 M 12% Microspheres 1.16 0.156 ± 0.02 N  6% Microspheres1.10 0.167 ± 0.02  5% Low Bulk Density CSH G 10% Low Bulk Density CSH1.12 0.197 ± 0.02 ¹The percent LDA in Formulations M, N and G replace anequivalent percentage of aggregate and/or binder in the control with noLDA, Formulation B.

CONCLUSIONS

In general, it will be appreciated that the preferred embodiments of thepresent invention, more particularly, a fiber-reinforced buildingmaterial containing additives of volcanic ash, hollow ceramicmicrospheres, or a combination of microspheres, volcanic ash and/orother additives, have several advantages over the prior art. Thesematerials have a low density compared to conventional fiber cementbuilding products. This enables production of a thicker product (e.g.,⅜″ to 1.0″) that is lighter and therefore easier to handle, cut, nailand install.

The materials also have improved wet-dry dimensional stability and thebuilding material's durability is improved such that building panels donot excessively shrink and crack. Also, excessive gaps between panels orplanks do not open up after changes in humidity or from wet to dryseasons.

With respect to at least the formulations and building productsincorporating hollow ceramic microspheres, the materials' freeze-thawresistance is maintained at lower density, unlike most inorganic densitymodified fiber cement materials. This gives these materials gooddurability in climates that experience frequent freezing and thawingconditions.

These materials incorporating microspheres also have improved fireresistance properties because of improved thermal dimensional stabilityrelative to typical low density additives. Thus, the materials arestable in building fires as a building component such that the materialcan maintain a shield to fire without cracking and falling apart andallowing fire to spread quickly.

The preferred embodiments have applicability to a number of buildingproduct applications, including but not limited to building panels(interior and exterior), tile backer board (walls and floors), siding,soffit, trim, roofing, fencing and decking. The embodiments illustratedand described above are provided merely as examples of certain preferredembodiments of the present invention. Various changes and modificationscan be made from the embodiments presented herein by those skilled inthe art without departure from the spirit and scope of the invention.

1. A building material, comprising: a fiber-reinforced cementformulation; and at least one low density additive incorporated into theformulation, wherein the at least one low density additive lowers thedensity of the building material as compared to a building materialhaving an equivalent fiber-reinforced cement formulation without the lowdensity additive, while at the same time the building material with theat least one low density additive has less than a 20% increase inmoisture expansion as compared to a building material having anequivalent fiber-reinforced cement formulation without the at least onelow density additive, wherein the density of the building material isless than 1.2 g/cm³.
 2. The building material of claim 1, wherein thedensity of the building material is about 0.9 to 1.1 g/cm³.
 3. Thebuilding material of claim 1, wherein the low density additive decreasesthe moisture expansion of the building material as compared to abuilding material having an equivalent fiber-reinforced cementformulation without the low density additive.
 4. The building materialof claim 1, wherein the median particle size of the low density additiveis between about 20 and 120 micrometers.
 5. The building material ofclaim 1, wherein the low density additive is volcanic ash incorporatedup to about 2 to 50 wt. %.
 6. The building material of claim 1, whereinthe low density additive comprises microspheres incorporated up to about2% to 90 wt. %.
 7. The building material of claim 6, wherein theformulation further incorporates a different low density additive inaddition to the microspheres.
 8. The building material of claim 7,wherein the different low density additive is a low bulk density calciumsilicate hydrate incorporated up to about 30 wt. %.
 9. The buildingmaterial of claim 1, wherein the formulation incorporates greater thanabout 4 wt. % fibers.
 10. A building material formulation used to form abuilding article, comprising: a hydraulic binder; an aggregate; fibers;and at least one low density additive incorporated into the formulation,wherein the at least one low density additive lowers the density of thebuilding article as compared to a building article having an equivalentfiber-reinforced cement formulation without the low density additive,while at the same time the building article with the at least one lowdensity additive has less than a 20% increase in moisture expansion ascompared to a building article having an equivalent fiber-reinforcedcement formulation without the at least one low density additive;wherein the density of the building article is less than 1.2 g/cm³. 11.The building material formulation of claim 10, wherein the hydraulicbinder is Portland cement incorporated into the formulation at a rangeof between about 5 to 80 wt. %.
 12. The building material formulation ofclaim 10, wherein the aggregate is a silica source incorporated into theformulation up to about 80 wt. %.
 13. The building material formulationof claim 10, wherein the fiber is cellulose fiber incorporated into theformulation at a range of between about 4 to 15 wt. %.
 14. The buildingmaterial formulation of claim 10, wherein the at least one low densityadditive is one or more of expanded volcanic ash with a bulk density ofabout 2 to 25 lbs/cu. ft, microspheres, ceramic microspheres, and lowbulk density calcium silicate hydrate.
 15. The building materialformulation of claim 10, wherein thermal shrinkage of the formed articleis between about 1% and 5%.
 16. A method of forming a low densitybuilding material, comprising: mixing a building material formulationwith water to create a slurry, wherein the formulation comprises ahydraulic binder, fibers, aggregate, and at least one low densityadditive, wherein the at least one low density additive lowers thedensity of the building material as compared to a building materialhaving an equivalent fiber-reinforced cement formulation without the lowdensity additive, while at the same time the building material with theat least one low density additive has less than a 20% increase inmoisture expansion as compared to a building article having anequivalent fiber-reinforced cement formulation without the at least onelow density additive; processing the slurry into a green shaped fibercement building article; and curing the green shaped fiber cementbuilding article to form the low density building material, wherein thelow density building material when formed has a density of less thanabout 1.2 g/cm³.
 17. The method of claim 16, further comprising mixingadditives with the hydraulic binder, fibers, aggregate, at least one lowdensity additive and water to create the slurry.
 18. The method of claim16, wherein moisture expansion of the formed low density buildingmaterial is about 0.17% or less.
 19. The method of claim 16, wherein theformed low density building material is cured by autoclaving.
 20. Themethod of claim 16, wherein thermal shrinkage of the formed low densitybuilding material is between about 1% and 5%.